Electric wave filter



Jan. 17, 1928. V v 1,656,225 v I M.. OSNOS ELECTRIC WAVE FILTER Filed Feb. 20. 192,5

- MENDEL osuos 93:1 is alien twain Patented Jan. 17, 1928.

UNITED STATES- 1,656,225 PATENT OFFICE.

MENDEL OSNOS, OF BERLIN, GERMANY, ASSIGNOB TO GESELLSCHAFT FI IR DRAHT- LOSE TELEGRAPHIE M. B. H. HALLESCHES, OF BEBLIN, GEBMANY, A CORPORATION OF GERMANY.

ELECTRIC WAVE FILTER.

Application filed February 20, 1923, Serial No. 620,221, and in Germany February 22, 1922.

In the art of high frequency transmission use is often made of atuned branch circuit which constitutes a short-circuit for waves of certain predetermined length and a cona siderable impedance for waves of all other lengths.

The usual exemplification of such a tuned short-circuit is that in which a self-induction and a capacity are connected in series. The combined self-induction L of this system, and, if the ohmic resistance is so small that for practical purposes it may be left out of consideration, the total impedance of the system is equal to zero for the frequency w or for the wave length A to which the system is tuned. On the other hand, for another frequency w or wave length this self-induction has the value:

This equation ,is positive for all waves A, which are shorter than M, and negative for all waves which are longer than A.,. -Th1s means that for )r the reactance is inductive, but for it is capacitive. However, in many instances a capacltive reactance is not only no obstacle for an alternating current but aids its passage, e. g. when'an E. M. F. is present which is strengthened by an advancing current.

In order to obviate the drawback which results from this, in accordance with the present invention, the short-circuit for the that it presents an inductive, reaetance for all the other undesired waves which are present in the system. This is always possible when e. g. an inductance or an inductance and a capacity are provided inseries with a branch comprising an inductance and a capacity connected in parallel therewith,-

desired wave is provided in such a manner having inductance and capacity arranged in series with each other and with a second system comprising inductance and capacity arranged in parallel, and

Figures at and are graphic illustrations of the reactance of the short-circuit shown in F ig.-3 plotted against thev wave length, for the ease in which the wave length of the system comprising inductance and capacity arrangedin series is smaller than the wave. length of the system comprising inductance and capacity arranged in parallel and vice versa.

In Fig. 1 a self-inductance L. is provided in series with a branch comprising a capacity Os and 'a self-induction L... If the natural wave length of the closed circuit C L is equal to then the impedance R, of the whole short-circuit arrangement may be represented for a desired frequency w or wave length A as follows:

L R,=wL -=w(L,,-- (2) From this we obtain the resulting equivalent self-induction L,. p

)3L r-Lr' t expressed in terms of the equivalent of inductance. The im edance has an inductive character fora pos tive value of L and a capacitive character for a negative value of L... As a function of A, L develops as shown in Fig. 2. For infinitely small values of A, L is equal to L It decreases when A increases, and is equal to zero for certain value of AK. Then as A still further increases L will be negative, i. e. the reactance will be capacitive. L approaches the value we when A appr aches the natural wave A, of the branch C L.. If A exceeds the value A then the value L, will become and remain positive because it decreases from plus and when the value A increases it approaches asymptotically the value L plus L...

In order to obtain the result aimed at by the present invention, the system must be so of the whole proportioned that two requirements will be satisfied:

First, for the predetermined wave A.

which filters through without being weakened, the impedance R, must present either a complete or partial capacitive short-circuit, i. e. A must be either equal to or slightly longer than AK which satisfied the equation L E (4) I xi l AK' is longer than any wave of the station shorter than A,..

Second, the individual wave A. of the branch L C must be longer than A., but shorter than the next longest wave which ma occur in the station.

t us assume, rfor instance, that in accordance with the present invention the seventh harmonic filters through the tuned short circuit without being weakened, but the other waves are destroyed and furthermore, that in the system we may generate only all the possible odd harmonics A3 A5 A7, A9, etc. Under these conditions the ve described system may be so tuned that first its AK be, ual-to or sli htly shorter than the seventh armonic A7, ut that under all circumstances it be longer than the ninth harmonic A9. Second A. must be longer than' A7 but shorter than A5. The resulting impedance R, will now be inductive for all harmonics which occur in the system except the seventh harmonic. v

In the. embodiment shown in Fig. 3, an additional capacity 1. is connected in series with L.. The natural wave length of the part L,, (3., is assumed to be A., that of the circuitC L., A as above, the corresponding individual frequencies being 0. and 0-- Disregarding ohmic resistances the impedance system may be expressed as follows and theresulting equivalent is: inductionz' t -i d-s i" Fig. 4 shows the development of the value A.islargerthanA.. Inbothcasesthefunc-' tion passes twice through zero from the positive to the negative. This means that in each case there are really two possible values of A, a smaller AKand a larger A... For

these the system presents a practically perfeetsho'rt circuit. The values ofA.andA.

without being ,r (2) The longer natural wave of the short- Fig. 3 must be so tuned that AK be (1 The shorter short-circuit natural wave AK of the system is so selected that it be equal to or slightlyshorter' than the harmonic A. which must be permitted to pass weakened.

circuit A, is so selected that it be longer than the longest wave occurring in the system, in a given case the basic wave A If, however, it is desired to permit also the passage of the basic wave without weakening it then A, is so selected that it be equal to or slightly shorter than A but longer than the next harmomc.

(3) Both natural waves A. and A, must'be longer than AK and shorter than A...

(4) A. must be longer than the harmonic AK the unweakened passageof which is desired but shorter than the next longest harmonic that may occur in the system.

If for instance, it is desired to permit the passage only of the seventh harmonic and that of the basic wave without materially weakening them,'and to weaken all the other harmonics, and if only all the odd harmonics may be produced in the system, then the short circuit arrangement in accordance git]: equ to or slightly shorter than A7 but longer than A9, A. be equal to or slightly shorter than A, butlo rtlianA3. A.andA.mustbebetween and A. and A. between A7 and A5.

The invention is of particular importance in one stage frequency amplification. See' for instance my application Serial No. 609,- 215, filed Dec. 27 1922, for circuit arrangement for high fieq choke coil, a plurality of difierent harmonics aretgroduced onl one of which is desired so talltheo ersmustbedestroyedor su ressed.

described my invention what I L In-an electric system having a plurality of wave lengths present, a filter, comprising a first circuit having an inducttalilnce alllld ahcapacity arranged in series wi eac ot er and I closed circuit in series with said first circuit, said closed circuit comprising an inductance and a capacity arranged n par- ;illll with each other, the elements of the r wave le to which the filter as a whole, is tuned is. shorter than the desired wave length but' longer than the undesired next uency sending stations, I wherebyby-means of a transformer or iron III so constituted that the shorter shortestwave length and the longer wave length to which the short circuit asa whole, is turlied is longer than any undesired wave lengt i. 1

2. In an electric system vhaving a plurality of wavelengths present, a filter, comprising a first circuit having an inductance and a capacity arranged in series with each other, and a closed circuit in series with said first circuit, said closed circuit comprising an inductance and a capacity arranged in parallel with eachxother, the elements of the filter being so constituted that the shorter wave length to which the filter, as a whole,'is tuned is shorter than the desired wave length but longer than the undesired next shortest wave length and the longer wave-length to which the short circuit, as a whole, is tuned is longer than any undesired wave length,

and the wave lengths to which the closed circuit is tuned and to which the first circuit is tuned lie between the two wave .but longer than the undesired next shortest wave length and thelonger wave length to which thefilter, as a whole, is tuned is slightly shorter than a second. desiredwave len ,-h but longer thanthe undesired wave lengths between the second desired wave length and the desired wave length.

- MENDEL OSNOS.

lengths to which the filter, as whole, is 

